The present invention relates to a noise reduction filter for use in electronic equipment for substantially reducing noises.
It has long been a usual practice to use a combined system of inductance and capacitance elements as a noise reduction filter, an example of which is shown in FIG. 1 of the accompanying drawings.
The prior art noise reduction filter shown by 1 in FIG. 1 comprises a metallic casing 2 accommodatihg therein a filter assembly including a pair of feed-through capacitors 4 and 5 spaced by and positioned on respective sides of a cylindrical magnetizable body 3 of, for example, ferrite, and a lead terminal member 6 extending completely through the filter assembly with its opposite ends situated exteriorly of the casing 2. The filter assembly together with the lead terminal 6 is confined within the casing 2 by means of a sealing resin 7 closing the opposite ends of the casing 2. In this construction, when an electric current flows through the lead terminal member 6, an electric field is developed in the magnetized body 3, thereby providing an impedance in a manner similar to a coil. An equivalent circuit of the noise reduction filter shown in FIG. 1 is illustrated in FIG. 2.
Another example of a prior art noise reduction filter is shown by 10 in FIG. 3. The noise reduction filter 10 comprises a casing 11 made of synthetic resin and having a cylindrical magnetizable body 12 of, for example, ferrite embedded therein, and a generally U-shaped lead terminal member 13 having one of its opposite arm portions extending through the casing 11 and then through a through-hole capacitor 15 and the other of the opposite arm portions extending through the magnetizable body 12 and then through a feed-through capacitor 14, the feed-through capacitors 14 and 15 being mounted on a chassis 16 and soldered respectively to the opposite arm portions of the lead terminal member 13. An equivalent circuit of the noise reduction filter 10 is similar to that shown in FIG. 2.
Both of the prior art filters 1 and 10 shown respectively in FIGS. 1 and 3 require the use of an increased number of the component parts and are, therefore, complicated and time-consuming to fabricate. Because of this, the prior art noise reduction filters discussed above are relatively expensive to manufacture.